Silicon (Si) waveguide-based photodiodes (PDs) may be a viable low-cost solution in high-speed optical transceiver products for applications such as data center interconnects. Additionally, Si PDs offer better ease of integration with low-cost Si-based electronics in very high-speed optical communication links that currently use III-V or Germanium (Ge)-based solutions for the photodiode.
However, Si PDs may demonstrate lower responsivity than Ge counterparts for a given p-n junction length. To compensate for this lower responsivity, Si PDs may be made longer, but the concomitant junction capacitance—which can be up to 8× larger than Ge PDs for achieving the same responsivity, may present a bottleneck in high-data-rate links. More specifically, this higher photodiode capacitance may lower the sensitivity of the optical receiver, as optical receiver sensitivity may be a function of photodiode capacitance in that the higher the photodiode capacitance, the lower the optical receiver sensitivity.